Jet engines of simple construction have been successfully built and operated. However, they are usually less fuel efficient than more complex engines or have some other serious shortcoming that hinders their acceptance in the marketplace.
A typical simple jet engine is disclosed in U.S. Pat. No. 3,093,962 to Gluhareff. A pre-heated gaseous fuel-air mixture is injected into an inlet passage at a velocity greater than the speed of flame propagation for that mixture so that the mixture cannot burn. The inlet passage is enlarged near the combustion zone so that the gases in the mixture slow down as they traverse the enlarged area. The speed drops to the speed of flame propagation as the mixture enters the combustion zone and, therefore, the mixture ignites as the gases flow through said zone; the expansion of gases thereby produced provides the thrust.
The fuel-air mixture of Gluhareff includes a liquefied petroleum gas such as propane; this eliminates the need for a compressor as a part of the engine. The fuel consumption rate of the Gluhareff design compares favorably with the fuel consumption rates of jet engines in common use, but such rate is still unacceptably high.
An ideal jet engine is of course unobtainable, but a consideration of the theoretical behavior of the exhaust gases of an ideal engine is instructive. If all of the energy provided by the combustion gases could be imparted to forward travel of the vehicle powered by the engine, the exhaust gases would not flow relative to the ground and would have a temperature equal to ambient. Thus, as a jet engine approaches ideal operating conditions, the flow rate of combustion gases therethrough slows and the temperature of said gases drops.
Conventional jet engines are high thrust, low efficiency devices. If the thrust or force F(t) developed by a conventional jet engine is plotted against time, a large amplitude, narrow bell curve results.
The area under the curve, found by integrating F(t) with respect to time between the interval t1 to t2, is equal to the change in momentum, or impulse of the engine. The narrowness of the bell curve, and the resulting low impulse, is a function of the limited time within which energy exchange collisions may occur. Note that substantially all of said energy exchange collisions are between the molecules of the exhaust gases, which travel at a very high speed, and the interior walls of the combustion chamber. This is the only significant source of energy exchange collisions in turbo, pulse, ram and all other types of jet engines heretofore known. Thus, the jet engines of the prior art are high in thrust but low in efficiency because the dwell time of the exhaust gas molecules in the combustion chamber is so short that secondary collisions between said molecules and ambient air are insignificant in number. Such lack of significant secondary collisions lowers the impulse of the known engines.
There is a need in the industry for a fuel efficient jet engine of simple construction that has operating characteristics that approach theoretically optimal conditions. More particularly, there is a need for a jet engine that provides more impulse than conventional engines. The instantaneous value of F(t) in such an engine would have a lower amplitude as compared to a conventional engine, but increased time would be available for energy exchange collisions to occur. Thus, the impulse would be greater. Such an improved engine would generate less thrust but would operate at a higher efficiency than conventional engines.
The teachings and suggestions of the prior art, when considered as a whole in accordance with the requirements of law, do not indicate to those of ordinary skill how the needed engine could be provided.